In recent years, there have been increasing demands that substrates made of organic materials such as plastics and inorganic materials such as glass be improved in terms of antifogging properties and antifouling properties.
To solve the fogging problems, a method has been proposed in which an antifogging coating containing a reactive surfactant and an acrylic oligomer is applied to provide enhanced hydrophilicity and water absorption (see, for example, Non Patent Document 1). The fouling problems have been addressed by methods in which the hydrophilicity of the surface of materials is enhanced so that fouling such as airborne hydrophobic substances which have become attached to surfaces such as exterior walls can be detached and removed from the surfaces by water spray or rainfall (see, for example, Non Patent Documents 2 and 3).
Further, hydrophilic materials have been proposed in which a monomer composition which is capable of crosslinking polymerization is applied onto the surface of a substrate and is incompletely polymerized while controlling the UV dose to form a crosslinked polymer, and subsequently a hydrophilic monomer is applied and UV rays are applied again to block- or graft-polymerize the hydrophilic monomer to the surface of the crosslinked polymer (Patent Document 1 and Patent Document 2).
However, because this simple block- or graft-polymerization of a hydrophilic monomer to the surface of a substrate results in the surface having a high surface energy though hydrophilic groups are present only on the surface, the surface becomes less slippery and causes friction which easily cuts and removes the hydrophilicity, posing a drawback in that the hydrophilicity is reduced in a short period and this does not allow the antifogging properties and fouling removal properties (antifouling properties) to be maintained for a prolonged time.
To solve the above problem, the present inventors have proposed monolayer films in which specific anionic hydrophilic groups have a concentration gradient (an uneven distribution) between the inside of the film and the film surface and the anionic hydrophilic groups are present in a higher concentration near the surface (Patent Document 3 and Patent Document 4). Films obtained by the present invention are component gradient films having hydrophilic groups also in their inside; are excellent in durability, transparent, very highly hydrophilic; are excellent in antifogging properties, antifouling properties, antistatic properties, quick-drying properties (whether the drying rate of attached water is fast or not), and chemical resistance; and, moreover, are rigid and excellent in abrasiveness.